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Refs #16043 -- Refactored internal fields value cache.

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* Removed all hardcoded logic for _{fieldname}_cache.
* Added an internal API for interacting with the field values cache.

Thanks carljm and MarkusH for support.
This commit is contained in:
Paulo 2016-06-04 16:10:37 -07:00 • committed by Tim Graham
parent 22ff86ec52
commit bfb746f983
11 changed files with 156 additions and 107 deletions
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45
django/db/models/query.py
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@ -72,7 +72,7 @@ class ModelIterable(BaseIterable):
if queryset._known_related_objects:
for field, rel_objs in queryset._known_related_objects.items():
# Avoid overwriting objects loaded e.g. by select_related
if hasattr(obj, field.get_cache_name()):
if field.is_cached(obj):
continue
pk = getattr(obj, field.get_attname())
try:
@ -1544,12 +1544,13 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
# callable that gets value to be matched for returned instances,
# callable that gets value to be matched for passed in instances,
# boolean that is True for singly related objects,
# cache name to assign to).
# cache or field name to assign to,
# boolean that is True when the previous argument is a cache name vs a field name).
# The 'values to be matched' must be hashable as they will be used
# in a dictionary.
rel_qs, rel_obj_attr, instance_attr, single, cache_name = (
rel_qs, rel_obj_attr, instance_attr, single, cache_name, is_descriptor = (
prefetcher.get_prefetch_queryset(instances, lookup.get_current_queryset(level)))
# We have to handle the possibility that the QuerySet we just got back
# contains some prefetch_related lookups. We don't want to trigger the
@ -1597,8 +1598,18 @@ def prefetch_one_level(instances, prefetcher, lookup, level):
if single:
val = vals[0] if vals else None
to_attr = to_attr if as_attr else cache_name
setattr(obj, to_attr, val)
if as_attr:
# A to_attr has been given for the prefetch.
setattr(obj, to_attr, val)
elif is_descriptor:
# cache_name points to a field name in obj.
# This field is a descriptor for a related object.
setattr(obj, cache_name, val)
else:
# No to_attr has been given for this prefetch operation and the
# cache_name does not point to a descriptor. Store the value of
# the field in the object's field cache.
obj._state.fields_cache[cache_name] = val
else:
if as_attr:
setattr(obj, to_attr, vals)
@ -1653,9 +1664,9 @@ class RelatedPopulator:
# model's fields.
# - related_populators: a list of RelatedPopulator instances if
# select_related() descends to related models from this model.
# - cache_name, reverse_cache_name: the names to use for setattr
# when assigning the fetched object to the from_obj. If the
# reverse_cache_name is set, then we also set the reverse link.
# - field, remote_field: the fields to use for populating the
# internal fields cache. If remote_field is set then we also
# set the reverse link.
select_fields = klass_info['select_fields']
from_parent = klass_info['from_parent']
if not from_parent:
@ -1674,16 +1685,16 @@ class RelatedPopulator:
self.model_cls = klass_info['model']
self.pk_idx = self.init_list.index(self.model_cls._meta.pk.attname)
self.related_populators = get_related_populators(klass_info, select, self.db)
field = klass_info['field']
reverse = klass_info['reverse']
self.reverse_cache_name = None
field = klass_info['field']
self.remote_field = None
if reverse:
self.cache_name = field.remote_field.get_cache_name()
self.reverse_cache_name = field.get_cache_name()
self.field = field.remote_field
self.remote_field = field
else:
self.cache_name = field.get_cache_name()
self.field = field
if field.unique:
self.reverse_cache_name = field.remote_field.get_cache_name()
self.remote_field = field.remote_field
def populate(self, row, from_obj):
if self.reorder_for_init:
@ -1697,9 +1708,9 @@ class RelatedPopulator:
if obj and self.related_populators:
for rel_iter in self.related_populators:
rel_iter.populate(row, obj)
setattr(from_obj, self.cache_name, obj)
if obj and self.reverse_cache_name:
setattr(obj, self.reverse_cache_name, from_obj)
self.field.set_cached_value(from_obj, obj)
if obj and self.remote_field:
self.remote_field.set_cached_value(obj, from_obj)
def get_related_populators(klass_info, select, db):